As an example of silica sols preparing by dispersing silica particles in a solvent, there has been known a silica sol comprising silica particles having a non-spherical structure such as a chain structure, a beads chain structure or a prolate spheroidal structure, and are dispersed in a solvent. These silica sols are used, for example, as various abrasives.
JP H01-317115A (Patent document 1) discloses a method of producing a silica sol including heteromorphic particles of silica with the ratio D1/D2 of more than 5 wherein D1 indicates a particle diameter measured by the image analysis method and is in the range from 40 to 500 millimicrons, and D2 indicates a particle diameter measured by the nitrogen gas adsorption method. The silica sol produced by the method of the present invention includes amorphous colloidal silica particles extending in one plain with homogeneous diameter in the range of 5 to 40 millimicrons observed by an electron microscope to make elongate shape dispersed in liquid medium. The method comprises the steps of: (a) adding a predefined volume of an aqueous solution containing water-soluble calcium salt, magnesium salt or the like in a predefined colloidal aqueous solution of activated silicic acid and agitating the mixture solution; (b) adding an alkali metal oxide, a water-soluble organic base, or a water-soluble silicate of the compounds is added so as to make the mole ratio of SiO2/M2O to be in the range of 20 to 200 (M indicates a molecule of the alkali metal oxide or the organic base); and (c) heating the mixture in the step at 60-150 degrees C. for 0.5-40 hours.
JP H04-65314A (Patent document 2) describes a method of producing a stable silica sol with the SiO2 concentration of 50% by weight or below and the ratio D1/D2 in the range from 3 to 5 wherein D1 indicates a particle diameter measured by the image analysis method and is in the range from 40 to 500 millimicrons, and D2 indicates a particle diameter measured by the nitrogen gas adsorption method. In the method, when addition of an aqueous solution of the active silicic acid to a sol of slender silica particles, collapse of colloidal silica particles in the feed sol does not occur, and the added active silicic acid is deposited via the siloxane bond on a surface of the original slender particle to provide colloidal silica having a slender form with the diameter increased from the original one.
JP H04-187512A (Patent document 3) discloses a method of producing a sol, in which chain-like silica particles are dispersed in a solvent, with the SiO2/M2O molar ratio in the range from 60 to 100. This method comprises the steps of adding a silicic acid solution into an aqueous solution of an alkali metal silicate with the SiO2 content in the range from 0.05 to 5.0% by weight to prepare a mixture solution with the SiO2/M2O ratio in the range from 30 to 60; adding a compound of one or more types of metals selected from the group consisting of Ca, Mg, Al, In, Ti, Zr, Sn, Si, Sb, Fe, Cu, and rare earth metals (before, during, or after addition of the silicic acid solution) to the mixture solution; maintaining the mixture solution at a temperature of 60 degrees C. or more for a prespecified period of time; and further adding a silicic acid solution into the mixture solution.
JP 3441142C (Patent document 4) proposes a polishing agent for semiconductor wafers comprising a stable silica sol in which a percentage of a silica particles having a major axis in the range from 7 to 1000 nm and a minor axis/major axis ratio in the range from 0.3 to 0.8 is 50% or more among all of the particles contained in the sol.
JP H07-118008A (Patent document 5) discloses a method of producing a sol of slender silica particles, and the method comprises the steps of adding an aqueous solution of a water-soluble potassium salt, a water-soluble magnesium salt, or a mixture thereof into a colloidal solution of active silicic acid; adding an alkaline substance into the obtained aqueous solution; heating a portion of the obtained mixture material up to 60 degrees C. or more to prepare a heel liquid (with the remaining portion defined as a feed liquid herein); adding the heel liquid to the feed liquid to evaporate water during the adding operation for obtaining a condensed liquid with the SiO2 concentration in the range from 6 to 30% by weight.
JP H08-279480A (Patent document 6) discloses that, in the aqueous solution of colloidal silica prepared by, for instance, (1) a method in which an aqueous solution of alkali silicate is neutralized with a mineral acid, an alkaline substance is added in the neutralized solution, and the mixture solution is heated for aging; (2) a method in which an alkaline substance is added in active silicic acid obtained by subjecting an aqueous solution of alkali silicate to positive ion exchange, and the mixture solution is heated for aging; (3) a method in which active silicic acid obtained by hydrolyzing alkoxy silane such as ethyl silicate is heated for aging; and (4) a method in which silica particles are directly dispersed in an aqueous medium, colloidal silica generally having the diameter in the range from 4 to 1,000 nanometers and preferably having the diameter in the range from 7 to 500 nanometers are dispersed in an aqueous medium, and that the colloidal silica aqueous solution has the concentration in the range from 0.5 to 50% by weight and preferably in the range from 0.5 to 30% by weight calculated as that of SiO2. The document also describes that forms of the silica particles include a spherical form, irregular form, a flat form, a plate-like form, a slender form, a fibrous form, and the like.
JP H11-214338A (Patent document 7) discloses a method of polishing a silicon wafer with a polishing agent containing colloidal silica particles as the main component, and the colloidal silica particles are obtained by methyl silicate refined by distillation is reacted to water in a methanol solvent in the presence of ammonia or in the presence of ammonia and ammonium salt as catalysts, and the major axis/minor axis ratio of the colloidal silica particle is 1.4 or more.
WO 00-15552A (Patent document 8) discloses a silica sol comprising spherical colloidal silica particles with the average diameter in the range from 10 to 80 nanometers and silica containing a metal oxide and bonding the spherical colloidal silica particles to each other, in which the ratio D1/D2 of the particle diameter (D1) measured by the image analysis method versus the average diameter of the spherical colloidal silica particles (D2: measured by the nitrogen adsorption method) is 3 or more, D1 is in the range from 50 to 500 nanometers, and the spherical colloidal silica particles are coupled to each other on one plain to form beads-like colloidal silica particles.
Patent document 8 also describes a method of producing the silica sol, and the method comprises the steps of (a) adding an aqueous solution of water-soluble metal salt to a predefined amount of a colloid aqueous solution of active silicic acid or an acidic silica sol so that a content of a metal oxide in the mixture solution against SiO2 in the colloid aqueous solution or in the acidic silica sol is in the range from 1 to 10% by weight to prepare a mixture solution 1; (b) adding an acidic sol of spherical silica particles with the average diameter in the range from 10 to 80 nanometers and with the pH in the range from 2 to 6 to the mixture solution 1 so that the weight ratio A/B (A indicating a content of silica originated from the acidic sol of spherical silica particles and B indicating a content of silica originated from the mixture solution 1) is in the range from 5 to 100, and at the same time so that a total content (A+B) of silica in a mixture solution 2 obtained by mixing the acidic sol of spherical silica particles with the mixture solution 1 is in the range from 5 to 50% by weight of SiO2 in the mixture solution 2; and (c) adding, a hydroxide of alkali metal, a water-soluble organic base or a water-soluble silicate salt the obtained mixture solution 2 so that the pH is in the range from 7 to 11, and heating the resultant mixture solution.
JP 2001-11433A (Patent document 9) describes a method of producing a sol of beads-like silica particles, and the method comprises the steps of an aqueous solution containing a water-soluble salt of bivalent or trivalent metal singly or in combination with salt(s) of other metal(s) in a colloid aqueous solution of active silicic acid containing SiO2 by 0.5 to 10% by weight and also having pH of 2 to 6 so that a content of the metal oxide (calculated as that of MO in a case of a salt of a bivalent metal, and of M2O3 in a case of a trivalent metal, and M indicating a bivalent or trivalent metal atom, and O indicating an oxygen atom) against SiO2 in the colloid aqueous solution of the active silicic acid and agitating the obtained mixture solution to obtain a mixture solution (1); adding an acidic sol of spherical silica particles with the average diameter in the range from 10 to 120 nm and also having the pH of 2 to 6 in the obtained mixture solution (1) so that a ratio A/B (weight ratio) of a content of silica originated from the acidic sol of spherical silica particles (A) and a content of silica originated from the mixture solution (1) (B) is in the range from 5 to 100, and at the same time so that a total content of silica (A+B) in a mixture solution (2) obtained by adding the acidic sol of spherical silica with the mixture solution (1) is in the range from 5 to 40% by weight calculated as that of SiO2 in the mixture solution (2) and agitating the resultant mixture solution; adding a hydroxide of alkali metal or the like in the mixture solution (2) so that the pH is in the range from 7 to 11 to obtain a mixture solution (3); and heating the obtained mixture solution (3) at a temperature in the range from 100 to 200 degrees C. for 0.5 to 50 hours to obtain a sol of beads-like silica.
JP 2001-48520A (Patent document 10) discloses a method of producing a silica sol in which amorphous silica particles with the average diameter in the range from 5 to 100 nanometers when observed with an electron microscope in the diametrical direction and the length in the range from 1.5 to 50 times of the diameter and also having a slender form are dispersed in a liquid-like dispersing medium. The method comprises the steps of hydrolyzing alkyl silicate with an acid catalyst without using a solvent in a composition with the silica concentration of 1 to 8 mole/litter, the acid concentration of 0.0018 to 0.18 mole/litter, and the water concentration of 0.2 to 1.5 mole/litters; then diluting the hydrolyte with water so that the silica concentration is in the range from 0.2 to 1.5 mole/litter; adding an alkaline catalyst so that the pH is 7 or more; and heating the solution to proceed polymerization of the silicic acid.
JP 2001-150334A (Patent document 11) discloses a method of producing a sol of silica particles each having a distorted form, and the method comprises the steps of adding an alkali-earth metal such as salts of Ca, Mg, and Ba to an acidic aqueous solution of active silicic acid with the SiO2 concentration of 2 to 6% by weight obtained by subjecting an aqueous solution of an alkali metal silicate such as water glass to the processing for removing positive ions at a weight ratio of 100 to 1500 ppm against SiO2 contained in the active silicic acid calculated as that of the oxide; furthermore adding the alkaline substance to the solution obtained in the step above so that the SiO2/M2O ratio (M denoting an alkali metal atom, NH4 or a quaternary ammonium group) is in the range from 20 to 150 to obtain an original heel liquid; repeating the same step to obtain, as a charge liquid, an aqueous solution of active silicic acid having the SiO2/M2O molar ratio (M denoting an alkali metal atom, NH4 or a quaternary ammonium group) in the range from 20 to 150 calculated based on the SiO2 concentration with the concentration of 2 to 6% by weight; and evaporating and removing water from the solution at a rate of 0.05 to 1.0 calculated as the weight ratio of SiO2 in the charge liquid/SiO2 in the original heel liquid per hour (this final step may optionally be eliminated).
JP 2003-133267A (Patent document 12) describes that the particles for polishing containing groups of particles having irregular forms in which two or more primary particles having the average diameter in the range from 5 to 300 nanometers are coupled to each other, especially particles for polishing in which a percentage of the primary particles constituting the groups of irregularly-formed particles against the total number of primary particles in the particles for polishing is in the range from 5 to 100% are effective as particles for polishing capable of being applied to polishing a surface of a substrate for flattening without causing dishing (excessive abrasion).
JP 2004-288732A (Patent document 13) discloses a slurry for polishing a semiconductor substrate containing non-spherical colloidal silica, an oxidizing agent, and an organic acid, and water in which a major axis/minor axis ratio of the non-spherical colloidal silica is in the range from 1.2 to 5.0, while also JP 2004-311652A (Patent document 14) discloses similar non-spherical colloidal silica.
JP 2002-3212A (Patent document 15) discloses a method of producing a sol of chained silica particles coated with silica-alumina. The method comprises the steps of (a) adding a silicic acid solution to an aqueous solution of an alkali metal salt with the Si contents of 0.05 to 5.0% by weight calculated as that of SiO2 to obtain a mixture solution with the SiO2/M2O mole ratio of 30 to 60 (M denoting an alkali metal or quaternary ammonium); (b) adding one or more metal compounds of bivalent to quadrivalent metals prior to, during, or after the step of adding the silicic acid solution; (c) leaving the resultant mixture solution at a temperature of 60 degrees C. or more for a prespecified period of time; (d) again adding the silicic acid solution to the reaction liquid to adjust the SiO2/M2O mole ratio to a range from 60 to 200; and (e) furthermore simultaneously adding an aqueous solution of an alkali silicate and an aqueous solution of an alkali aluminate to the reaction liquid keeping pH of the liquid in the alkaline region.
JP H03-257010A (Patent document 16) describes an example of silica-based particles each having projections on a surface thereof, and the silica particles have, on a surface thereof, successive irregular projections each having the size in the range from 0.2 to 5 μm when observed with an electron microscope, the average diameter in the range from 5 to 100 μm, the specific surface area of 20 m2/g or below when measured by the BET method, and the pore volume of 0.1 mL/g or below.
JP 2002-38049A (Patent document 17) describes silica-based particles each having a substantially spherical and/or semi-spherical projections on an entire surface of the core particle in which the projections are bonded to the core particles by chemical bond, and also describes silica-based particles each having a substantially spherical and/or semi-spherical projections on an entire surface of the core particle in which the projections are chemically bonded to the core particles. Furthermore, the document describes a method of producing silica-based particles, and the method comprises the steps of (A) generating polyorgano-siloxane by hydrolyzing a specific alkoxysilane compound and condensating the hydrolyte, (b) subjecting the polyorgano-siloxane particles to the surface processing with a surface absorbent; and (c) forming projections on the entire surface of the polyorgano-siloxane particle having been subjected to the surface processing in step (b) above with the alkoxysilane compound.
JP 2004-35293A (Patent document 18) discloses silica-based particles each having substantially spherical or semi-spherical particles on the entire surface of a maternal particle thereof. The silica-based particle is characterized in that the projections are chemically bonded to the maternal particles, and a compressive elasticity modulus of the material particle when compressed by 10% is different from that of the projection.
However, the articles described in JP H03-257010A (Patent document 16) are mainly those having the average diameter in the range from 5 to 10 μm, and the silica-based particles disclosed in JP 2002-38049A (Patent document 17) are only those with the average diameter substantially in the range from 0.5 to 30 μm, and what is described above is also applicable to JP 2004-35293A (Patent document 18).    [Patent document 1] JP H01-317115A    [Patent document 2] JP H04-65314A    [Patent document 3] JP H04-187512A    [Patent document 4] JP 3441142C    [Patent document 5] JP H07-118008A    [Patent document 6] JP H08-279480A    [Patent document 7] JP H11-214338A    [Patent document 8] WO 00-15552A    [Patent document 9] JP 2001-11433A    [Patent document 10] JP 2001-48520A    [Patent document 11] JP 2001-150334A    [Patent document 12] JP 2003-133267A    [Patent document 13] JP 2004-288732A    [Patent document 14] JP 2004-311652A    [Patent document 15] JP 2002-3212A    [Patent document 16] JP H03-257010A    [Patent document 17] JP 2002-38049A    [Patent document 18] JP 2004-35293A